1. Field of the Invention
The invention pertains to the field of electronic device fabrication and packaging and more particularly to design of bond wire configurations.
2. Background Information
Wire-bonding is a widely used electrical packaging technique for interconnecting a semiconductor device with a mounting. However, wire-bonding becomes more problematic as data rates increase (e.g., at higher frequencies) due to parasitics. Parasitics take many forms, one of which is excessive or variable impedance. A solution to control or reduce parasitic effects includes designing the device to reduce bond wire lengths, thereby reducing the bond wire inductance. Where a bond wire connection is desirable at the device edge, short bond wire lengths are possible and have utility. However, there are device applications were a bond wire is required on the device interior. Device designs and design techniques to reduce or control parasitic effects for these configurations are needed. Additionally, device designs and techniques to reduce or control parasitic effects with bond wire attachments at device edges are valuable.
In one aspect, the invention discloses an electronic device with a desired bond wire transmission line impedance. Bond wire transmission line impedance in this regard is well known, and is represented by (inductance per unit length/capacitance per unit length)xc2xd. Wire bonds connect a first region, such as a microstrip connector on a mounting, with a second region, such as a connection on a semiconductor chip. The wire bonds are separated and traverse over a substrate region on the semiconductor chip. The desired bond wire impedance is achieved by adjusting or configuring the separation or distance between the bond wires (wire center-center distance) and the separation between the bond wires and the substrate (substrate-wire gap), with consideration for the bond wire diameter, and the device substrate dielectric constant. This aspect of the invention has an advantage of providing a device with bond wires that have variable center-center separation but provide a desired impedance.
In another aspect, the invention discloses an electronic device with a desired bond wire impedance. Wire bonds connect a first region, such as a microstrip connector on a mounting, with a second region, such as a connection on a semiconductor chip. The wire bonds are substantially parallel and traverse over a substrate region on the semiconductor chip at a substantially constant distance. The desired bond wire impedance is achieved by adjusting or configuring the separation or distance between the bond wires (wire center-center distance) and the separation between the bond wires and the substrate (substrate-wire gap), with consideration for the bond wire diameter, and the device substrate dielectric constant. This aspect of the invention has an advantage of providing a device using parallel bond wires uniformly separated from a device substrate to provide a desired impedance.
In another aspect, the invention discloses a design method whereby a desired impedance is achieved in at least two bond wires that connect a first and second region on the device. The bond wire diameter is determined, the device substrate dielectric constant is determined and these values are used in conjunction with the separation between the bond wires and the separation between the bond wires and the substrate to provide the desired impedance. This aspect of the invention has an advantage of providing a device design technique to provide a desired bond wire impedance by configuring packaging variables.
The foregoing specific aspects and advantages of the invention are illustrative of those which can be achieved by the present invention and are not intended to be exhaustive or limiting of the possible advantages that can be realized. Thus, the objects and advantages of this invention will be apparent from the description herein or can be learned from practicing the invention, both as embodied herein or as modified in view of any variations which may be apparent to those skilled in the art. Accordingly the present invention resides in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.